The present invention relates to a perfected electromagnetic fuel metering and atomizing valve for a vehicle fuel supply system.
Valves of the aforementioned type substantially comprise a plunger for controlling fuel passage through an injection orifice, and which, by means of an electromagnet, is moved inside an axial seat in the valve body, between a closed position wherein the injection orifice is closed, and an open position wherein fuel is allowed to flow through the orifice. The plunger is defined by a cylindrical lateral surface mating in sliding manner with a corresponding cylindrical surface of the seat in the valve body.
Valves of the aforementioned type present several drawbacks.
Firstly, fuel leakage frequently occurs between the bottom surface of the plunger and the corresponding supporting surface in which the injection orifice is formed. Secondly, the mating surfaces of the plunger and/or seat are subject to severe in-service wear, particularly localized wear on the edges of the mating surfaces. Thirdly, the manufacture of certain members and components of the valve, particularly the plunger and the portion of the valve body in which the plunger slides, involves accurate machining to precise tolerances. Finally, manufacture of the above components requires the use of high-cost materials, processing for hardening the sliding surfaces, or post-machining processing for depositing layers of hard material for reducing wear of the sliding components.
All the above drawbacks are caused by failure to provide for accurately guiding axial displacement of the plunger between the open and closed positions, and so maintaining the axis of the plunger perfectly parallel to that of the sliding seat and, consequently, of the valve. In fact, during operation of the valve, the plunger is subjected to two non-coplanar forces perpendicular to the valve axis. One of these is due to the transverse component of the inertial forces produced by vibration of the engine and by other in-service movements of the vehicle, which component may be imagined as being applied at the barycenter of the plunger and, consequently, as lying substantially in a plane perpendicular to the valve axis and containing the barycenter of the plunger.
The other force is the transverse component of the electromagnetic forces to which the plunger is subjected in the magnetic circuit of which it forms part, which component may be said, to a fairly good degree of accuracy, to act in a plane perpendicular to the valve axis and located at the mid plane of the cylindrical seat in which the plunger slides. By virtue of the above two components operating in non-coincident planes, the plunger is subjected to a torque which tends to rotate it about axes perpendicular to the valve axis, so that the axis of the plunger fails to be maintained parallel to that of the sliding seat, due to the radial clearance normally allowed between the plunger and seat for enabling the former to slide in relation to the latter. The above drawbacks are nevertheless also encountered even in the presence of very little radial clearance.